Purified water and processed steam are used in many oil refinery operations. Purified water is often used in heat exchangers and various water-wash operations. Processed steam is used in pipestills, cokers, fluid catalytic cracking units, mid-distillate strippers, light distillate strippers and other applications. As a result of this use, significant quantities of contaminated sour refinery water are produced. The sour water may contain suspended and dissolved impurities, such as phenols, sulfides, ammonia, and other hydrocarbons. The processing of the sour water can generate a waste stream that is highly concentrated in ammonia, which must be disposed of in an environmentally safe manner. The sour water is typically stripped with steam to remove the impurities. In a two-stage stripping process, the sulfides are substantially stripped out in the first stage for processing in a sulfur plant. In the second stages a waste stream consisting substantially of ammonia and steam is produced. The waste stream containing ammonia may be burned, but an undesirable by-product of this incineration is the generation of oxides of nitrogen (NOx) (i.e., NOx emissions). NOx emissions are highly regulated by regulatory agencies.
One approach for treating waste streams containing high concentrations of nitrogen, while minimizing NOx emissions, is offered by the John Zink Company. The John Zink Company's NOxidizer™ system uses a three stage incineration process to limit NOx formation. In the first stage, the waste stream and fuel are burned with less than the stoichiometric requirement of oxygen. The products of the combustion are cooled in the second stage and reoxided in the third stage. The three stages are carried out in a series of refractory-lined vessels along with a high-intensity burner. While the process is effective in disposing of nitrogen-containing waste streams and reducing NOx emissions, the process requires a significant investment of capital along with significant yearly operating costs.
There is a need for a lower cost alternative for processing a nitrogen-containing waste stream while minimizing NOx emissions.